With increasing miniaturization of electrical and electronic devices, and increasing packing density in combining devices into assemblies, there is growing commercial interest in means other than traditionally used soldering for making electrical interconnections. Prominent among such means are composite media in which electrically conducting particles are embedded in a nonconductive matrix material, such media forming, e.g., viscous, complaint, or hardened structures between components bearing contact pads.
Interconnection media may take a variety of forms and have been made having conductivity in one, two, or three mutually perpendicular directions. A particularly important category of interconnection media takes layer or sheet form, in which case it is customary to designate directions such that x- and y-directions lie in the plane of the sheet or layer. Some such interconnection media have z-direction conductivity only, others have z- and y-direction conductivity, and isotropically conductive media have x-, y-, and z-direction conductivity. For an instance of each of these cases see, respectively,
U.S. Pat. No. 4,548,862, "Flexible Tape Having Bridges of Electrically Conductive Particles Extending Across Its Pressure-Sensitive Adhesive Layer", issued Oct. 22, 1985 to R. B. Hartman;
U.S. Pat. No. 4,546,037, "Flexible Tape Having Stripes of Electrically Conductive Particles for Making Multiple Connections", issued Oct. 8, 1985 to T. W. King et al.; and
A. Malliaris et al., "Influence of Particle Size on the Electrical Resistivity of Compacted Mixtures and Polymeric and Metallic Powders", Journal of Applied Physics, Vol. 42 (1971), pp. 614-618.
In the following, particular attention is accorded to interconnection media having at least two directions of conductivity. With respect to such media, the invention is motivated in part by a desire for reducing the concentration of conductive particles in a composite medium so as to more nearly retain in the composite medium the mechanical properties of a matrix material.